Amplifier



R. WEBER AMPLIFIER April 5, 1938.

Filed Aug. 15, 1935 INVENTOR, RUDOLF WEBER ATTORNEY.

Patented Apr. 5, 1938 UNITED STATES AMPLIFIER Rudolf Weber, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Gerin any Application August 15, 1935, Serial No. 36,285

In Germany August 29, 1934 3 Claims.

This invention relates to a signal amplifier in which, at the appearance of a frequency corresponding to a predetermined signal, an indicating lamp will be illuminated.

It is an object of my invention to improve upon signal responsive devices of heretofore known types by providing a system in which the gain in an amplifier is variablycontrolled by the received signals so that if the signal is of one frequency, this gain would be increased, whereas if it is of another frequency, the gain would be decreased.

Another object of my invention is to provide a signal amplifier feeding into an output circuit which contains preferably a system of glow discharge tubes, and to provide the means for exciting these tubes selectively according to the potential drop which is produced across their electrodes.

Another object of my invention is to provide a s stem of the character mentioned in the foregoing, in which suitable filtering means are also provided in combination with rectifiers such that a grid biasing circuit in the amplifier may be controlled positively or negatively according to the frequency of the received signal which is passed through one or the other of the filters respectively. By achieving the objects of my invention the heretofore known arrangements will be seen to have been improved upon in such manner that certain disadvantages of the prior art will be overcome. Among these disadvantages may be mentioned the following:

1. In practice, a single filter means is not sufiicient to obtain a definitefrequency, and in order to provide a satisfactory selectivity, several, at least two, filter means should be placed in series. This however entails the necessity of a considerable amount of material.

At the arrival of very strong signals. at the input, it can also happen that other glow tubes will be simultaneously illuminated thus causing erroneous signaling, unless a special amplitude control is provided.

2. Glow tubes as used in systems of the prior art in order to be sensitive to signals have usually been biased close to the ignition potential and sometimes above the extinction potential and for this reason they were subject to ignition improperly, incident to disturbing impulses. If automatic extinction devices were provided, these would tend to complicate the device and add to its weight as well as its cost.

The invention will now be described in detail, reference being made to the accompanying drawing in which Fig. 1 shows one embodiment of my invention; and

Fig. 2 shows a modification thereof.

Referring first to Fig. 1, I show a preferred embodiment of my system in which signals may be impressed upon the primary of a transformer l and transferred-thence to the input circuit of an amplifier tube 2. This tub'e may be a triode, if desired, but preferably a screen grid tube may be used as shown. In the output circuit of the tube 2 I may insert two gaseous discharge tubes 4 and, 5 in series with a choke coil 3. The cathode of the tube 4 and the anode of the tube 5 are interconnected, andlikewise the cathode of the tube 5 and the anode of the tube 4 are interconnected. Between the cathode of the tube 2 and one of the common connections between the tubes 4 and 5, I insert a portion l5 of the direct current anode potential source which is to be .fed to the anode of the tube 2 through a resistor 6 and thence through the choke coil 3. Another portion [6 of this direct current anode source lies between the first mentioned portion thereof and the resistor 6. The input circuit of the tube 2 includes a grid bias resistor l3 and a. capacitor l2 shunting the same.

The values of the anode potential sources I 5 and Hi, the ohmic resistance values of the resistor 6 and the choke coil 3, and the value of the grid bias resistor l3 are all so chosen that the drop of potential across the resistor 6, when the tube 2 is acting normally and without the impress thereon of any signal, is about equal to the potential drop internally of the tube 2, that is to say, between the anode and the cathode thereof. In making this statement, the ohmic resistance value of the choke coil 3 may be neglected. Also the fixing of values for the anode potential sources l5 and I6 and for the resistor 6 must be determined with due consideration for the ignition and extinction voltage ratings of the tubes 4 and 5. In other words, the system must be made stable when no signal is coming in so that neither one of the tubes 4 or 5 will be ignited by a. normal potential drop across the resistor 6 due to normal current flow in the tube 2. If, however, the impedance of the tube 2 is either increased or decreased then it will be possible to igniteone of the tubes 4 or 5 selectively. The means for accomplishing this result include a gain control device in circuit with the grid lead to the tube 2.

This gain control device is coupled to the output circuit of thetube 2 by means of a capacitator I so that output energy, or at least some of it, may be fed through the primaries of two transformers which are respectively included in two resonant circuits 8 and 9, one of them being tuned to a predetermined frequency to be used for signals having one significance and the other being tuned to a different frequency so that it will respond to signals having another frequency significance. Energy of the first mentioned signalling frequency may therefore be fed through the resonant filter system 8 and through a rectifier l which tends to lower the grid bias potential on the tube 2 and thus to reduce the current fiow therein. Since the tube impedance rises in response to signals of this frequency, it will be seen that the potential on the anode of the tube will be increased, and such increase being above the ignition voltage of the tube 5, this tube will nowbecome ignited in response to the signal.

A signal of the second mentioned frequency may likewise be received and passed through the filter system 9, in which case the output energy therefrom may be fed through the rectifier ll so as to render the grid of the tube 2 more positive. This will lower the potential of the anode of the tube 2 and correspondingly render the cathode of the glow tube 4 more negative, as a result of which the tube 4 will now become ignited and the tube 5, if it had previously been ignited, will now be extinguished. The increased current flow in the tube 2 is at least partly absorbed by a current flow through the tube 4, excitation being provided by means of the battery l5.

Referring now to Fig. 2, I show a modification in which the glow tubes 4 and 5 are placed in series with the transformer primaries of the filter systems 8 and 9. The resistor 6 occupies the same position relatively to the connections of the tubes 4 and 5as is shown in Fig. 1. In fact, the operation of the circuit is similar in most respects to that of Fig. l and accordingly further description of this modification is not necessary.

I claim:

l. A signal responsive device comprising an amplifying electron discharge tube having a cathode, an anode and at least one grid; a direct current source and an ohmic resistance in circuit between the cathode and anode; a pair of asymmetrical glow discharge tubes each connected in shunt with said resistance and with a r '-:tion of said direct current source; means including resonant circuits coupled to the anode of said amplifying tube for providing a grid biasing control potential thereto and means including a rectifier interposed between each of said resonant circuits and the grid of said amplifying tube for producing a more negative bias on said grid in response to a signal of a frequency to which one of said circuits is resonant, and a more positive bias in response to a signal of a frequency to which the other of said. circuits is resonant, whereby the conductivity of said amplifying tube is caused to be varied above and below a level of no-signal-response, and one or the other of said glow discharge tubes is correspondingly ignited.

2. In a diiferentiallyresponsive signal indicator, a pair of gaseous discharge tubes each having an anode and a cathode, the anode of each tube being connected to the cathode of the other, an amplifier tube network having an input circuit and an output circuit, said gaseous tubes being parallel-connected in said output circuit, means including resonant filter systems coupled to said output circuit and unidirectional devices each connected in an opposite sense to that of the other and between said filter systems and said input circuit for varying the control grid bias positively in response to a signal of one frequency and negatively in response to a signal of a different frequency, and means for causing the resulting variation in the tube impedance of said amplifier network to produce an ignition voltage across one of said gaseous tubes when the amplifier tube impedance is lowered and for producing an ignition voltage across the other of said gaseous tubes when the amplifier tube impedance is raised.

3. A receiving system having an electron discharge tube amplifier in combination with a pair of glow tubes and a pair of resonant circuits coupled to the output circuit of said amplifier, a device for exciting said glow tubes selectively in response to the impress of signals of different frequency characteristics upon said electron discharge tube amplifier, said device including means for rectifying a portion of the output energy from said amplifier and for producing theremeans for causing the resultant increase or decrease in conductivity of the electron discharge path in said amplifier to control the potential drop across the electrodes of said glow tubes in such manner that one of them is ignited in response to a signal of the first said frequency and I the other of said glow tubes is ignited in response to a signal of the second said frequency.

RUDOLF WEBER. 

